Remote access solutions enable workers away from a company to securely access the company network. Through the use of IPSec VPNs or SSL VPNs remote users are able to access a company network in a secure manner. Access from a client device may be routed through one or more gateway servers which are utilized in maintaining the remote access session. With conventional remote access solutions, failure in a gateway server maintaining the remote access session results in a terminated session and lost data.
To address the issue of gateway server failure, a number of different conventional techniques have been applied in an attempt to ensure redundancy and full availability of system resources in the event of hardware or software failure. In an active/passive server arrangement an active server hosts a number of executing processes and applications. The active server may be hosting an IPSec VPN-based session or an SSL based session. One or more other servers are designated as backup or “failover” servers. The failover servers include the capability of executing the same applications and processes that are executing on the active server but the failover server(s) do not execute the applications and processes until notified of a problem with the active server. The failover servers are known as “passive” servers in this arrangement because they may be thought of as quietly waiting to execute the applications and processes that are being executed on the active server while the backup server is operating in failover mode. Once notified of a problem with the active server, one of the failover servers is selected as the new active server, receives the last saved state/session information from the formerly “active” server and proceeds to execute in the manner in which the previous active server was executing prior to the detected failure/problem. Unfortunately, the active/passive arrangement results in a loss of data during the transition from the first active server to the newly designated active server.
It will be appreciated that the failover servers may be located on either the same or a separate physical node. An implementation that includes a failover server on the same physical node runs the risk that the failure causing the failover is associated with a physical node element that will also impact the failover server. Locating the failover server on a separate physical node that includes separate physical resources (e.g. memory, disk arrays, motherboard, etc.) lowers the risk of a single physical element causing both the active and failover servers to fail but increases the cost of the overall system in both hardware acquisition and management.
Another technique to provide redundancy amongst servers is to arrange servers in an active/active arrangement. In an active/active arrangement, both the active and passive failover servers are executing the same set of applications and processes. When the first active server goes down, the second active server allocates resources to those application instances and processes that were previously being handled by the failed server.
Unfortunately, neither the active/passive nor the active/active failover server arrangement lend themselves to preserving session state for a remote access session. Neither conventional failover implementation allows a remote session state to be mirrored in a failover server such that the failover server may be transitioned to without terminating the existing session and losing session data. It would be desirable to be able to preserve an existing remote session and its session data in the event of a failure affecting an active server hosting the remote session.